The present invention relates to a surface-mounted chip-type LED and a method for manufacturing the same, and is used as a light source in various types of display panels, backlighting for liquid-crystal display apparatuses, lighting switches, and the like.
Chip-type LEDs have conventionally been used as a light source in various types of display panels, backlighting for liquid-crystal display apparatuses, lighting switches, and the like.
FIG. 12 shows an example of the structure of a conventional chip-type LED.
The conventional chip-type LED has a two-layer structure including insulating substrates 81 and 82, and is configured such that a through hole 83 is formed in the upper insulating substrate 82, a wiring pattern 84 is formed such that it extends to the bottom within the through hole 83 (i.e., the upper surface of the lower insulating substrate 81), an LED chip 85 is mounted on the wiring pattern 84 within the through hole 83, the LED chip 85 is connected to another wiring pattern 86 with a fine metal wire (Au wire, etc.) 87, and the surface of the insulating substrate 82 is encapsulated in a transparent resin 88 so as to include the LED chip 85 and the fine metal wire 87. Chip-type LEDs having a structure as described above are disclosed in, for example, JP 2001-160629A and JP 2006-190764A.
However, a chip-type LED of the conventional structure requires two insulating substrates 81 and 82, and the lower insulating substrate 82 is required to have a minimum thickness necessary to carry the LED chip 85 because the LED chip 85 is mounted on the lower insulating substrate 82, and thus problems exist such as difficulties achieving a thin LED and high costs.
In order to solve this problem, JP H07-235696A discloses a wiring structure for a semiconductor device and a method for forming the same. According to JP H07-235696A, a semiconductor device is obtained by forming a through hole on the surface side of an overall thin copper-laminated substrate obtained by laminating thin copper plates on the surface and undersurface of an insulating resin substrate, mounting an LED chip on an exposed surface of the lower copper plate inside the thorough hole, and performing encapsulation with a single resin layer so as to cover the through hole.
JP H07-235696A that discloses this thin semiconductor device doesn't reveal a technique for letting the semiconductor device to emit white light. In order to cause the semiconductor device to emit white light, it is only necessary to include a yellow fluorescent material in the single resin layer. To form the encapsulating resin, there is a method in which a fluorescent material is included in a semi-cured tablet resin (a resin for transfer molding) and transfer molding is performed to obtain a white light-emitting chip LED. This method provides very good workability and thus is suitable for mass production.
However, due to the nature of transfer molding, the concentration of the fluorescent material varies significantly from place to place, and it is impossible to avoid variations in chromaticity, which is a very important property of white light-emitting LEDs.
In addition, there is a limitation on the production method of such a table resin (the quantity produced at one time is very large), so the blending ratio of the fluorescent material cannot be flexibly changed.
Moreover, it is generally known that the light emitting efficiency can be increased to a maximum by disposing the fluorescent material near the LED chip. When transfer molding is performed, however, the fluorescent material spreads not only near the LED chip but also throughout the entire molding resin, making the light emitting efficiency low relative to the amount of the fluorescent material used. Also, color nonuniformity is likely to occur due to sedimentation of the fluorescent material and the like.
Silicone resins having a high heat resistance are commonly used as an encapsulating resin material, but it is impossible to perform transfer molding with a silicone resin because transfer molding employs a resin that can be in a semi-cured state. It is possible to perform transfer molding with a resin that is liquid in an uncured state such as silicone resin, but a highly sophisticated technique is required because air bubbles are easily included in a low viscous liquid resin and a dedicated apparatus is necessary that includes a means for preventing the inclusion of air bubbles.
Furthermore, silicone resins have a rigidity lower than that of epoxy resins, and in a chip-type LED structure in which a member for protecting the encapsulating resin, such as a reflective material, is not provided around the encapsulating resin, the encapsulating resin is easily scratched and deformed (e.g., due to direct contact of the upper surface with a mounting device). For this reason, silicone resins are not suitable for use as an encapsulating resin.
Nonetheless, the resin near the chip is degraded significantly by light (ultraviolet, near-ultraviolet to blue light) emitted from the chip before conversion by the fluorescent material. Accordingly, a silicone resin, which has better light resistance than an epoxy resin, should be used to encapsulate the periphery of the chip.